Apparatus for controlling electric water pump of hybrid vehicle and method thereof

ABSTRACT

The present invention relates to a water pump control apparatus of a hybrid vehicle and a control method thereof. An exemplary apparatus according to the present invention includes a thermostat determining a circulation path of the coolant, a coolant temperature sensor, a motorized water pump configured to pump a coolant, and a control portion for controlling the motorized water pump to circulate the coolant, if the hybrid vehicle enters into an EV mode or an idle engine stop mode if the coolant temperature exceeds a predetermined temperature. An exemplary method of the present invention includes the steps of suspending operation of the motorized water pump if the coolant temperature is less than a predetermined value until a cooling fan is operated, and controlling a driving speed of the motorized water pump according to a load of the cooling fan in operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0028562 and 10-2010-0040328 filed in the Korean Intellectual Property Office on Mar. 30 and Apr. 29, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a motorized water pump applied to a vehicle, in particular a hybrid vehicle.

(b) Description of the Related Art

Hybrid vehicles have been developed and are increasingly mass produced to be sold and driven by consumers. There are various kinds of hybrid vehicles. A typical hybrid vehicle generally includes an engine and a motor. When the hybrid vehicle is in electric vehicle mode (EV mode), only the motor is operated. Alternatively, when the hybrid vehicle is in hybrid vehicle mode (HV mode), both the motor and the engine are in operation.

A hybrid vehicle typically generates electricity through regenerative braking which charges the battery, and reduces fuel consumption and exhaust gas through an ISG (idle stop and go) system. The hybrid vehicle forcibly circulates a coolant so as to prevent the engine from being overheated. Accordingly, if the hybrid vehicle enters into the EV mode or the ISG mode in a condition that the coolant temperature is high, the water pump operated by the engine stops operating such that the coolant is not circulated. The engine is repeatedly re-started with a high temperature coolant because of the idle engine stop mode and the HV mode, as a result, if the load of the engine is rapidly raised after restarting the engine, the coolant can be overheated.

If a user requests use of a heating system during the EV mode or the idle engine stop mode, a problematic situation may arise where the hot coolant does not circulate through the heating system. In addition, the EV mode and the idle engine stop mode cannot be performed under cold coolant conditions, until the engine is warmed up.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide an apparatus for controlling an electric water pump of a hybrid vehicle. In particular, the apparatuses and methods provide the advantages of securely controlling the coolant temperature of an engine by forcibly operating a motorized water pump when the engine coolant temperature is high and an EV mode or an idle engine stop mode is performed, so that the engine does not become overheated.

The present invention provides a motorized water pump which may be continuously operated in order to circulate the coolant so as to securely operate an interior room heating apparatus. In addition, the present invention provides variable control of the motorized water pump. The motorized water pump may be varied by applying a factor value mapped according to a vehicle speed in a condition where the coolant temperature is high.

The present invention may also provide optimized cooling efficiency by variably controlling a motorized water pump according to a load of a cooling fan in a condition that a motorized water pump is stopped until the radiator cooling fan is operated after starting of a cold engine.

According to one embodiment of the present invention, a motorized water pump control apparatus of a hybrid vehicle includes a thermostat which determines a circulation path of the coolant, a coolant temperature sensor detecting a coolant temperature, a motorized water pump configured to pump a coolant, and a control portion controlling the motorized water pump to circulate the coolant, if the hybrid vehicle enters into an EV mode or an idle engine stop mode if the coolant temperature exceeds a predetermined temperature.

In another embodiment, the control portion may drive the motorized water pump if operation of a heating apparatus is demanded in an EV mode or an idle engine stop mode. In yet another embodiment, the control portion may vary a driving speed of the motorized water pump according to a vehicle speed if the vehicle enters into an idle engine stop mode in a condition that the coolant temperature exceeds a predetermined temperature value.

In a further embodiment, the control portion may enter into a limp home mode, output an alarm message, and drive the motorized water pump to circulate the coolant if an error is detected from the cooling system.

A motorized water pump control method of a hybrid vehicle is also provided. In one embodiment of the present invention, the method includes the steps of determining whether a hybrid vehicle enters into an EV mode or an idle engine stop mode, determining whether the coolant temperature exceeds a predetermined value if the hybrid vehicle is in the EV mode or the idle engine stop mode, driving the motorized water pump if the coolant temperature exceeds the predetermined value and turning off the motorized water pump if the coolant temperature is less than the predetermined value, and varying a driving speed of the motorized water pump according to a vehicle speed if the vehicle speed is larger than a predetermined value in a condition that the motorized water pump is being driven.

In another embodiment, the motorized water pump may be driven to circulate the coolant if operation of a heating apparatus is demanded in an EV mode or an idle engine stop mode.

In a further embodiment, the motorized water pump control apparatus of a hybrid vehicle may include a thermostat determining a circulation path of coolant according to the coolant temperature exhausted from the engine, a radiator emitting heat absorbed in the coolant, a cooling fan that is disposed at one side of the radiator to blow air, a motorized water pump that is disposed between the engine and the thermostat to circulate the coolant, and a control portion that turns the motorized water pump on/off according to an operating load of the cooling fan.

In one embodiment, the control portion may monitor environmental conditions and driving conditions of the engine, and enters into a limp home mode so as to operate the motorized water pump if an error is detected from the monitored data.

In another embodiment, the control portion may stop operation of the motorized water pump until the cooling fan is operated for the first time after ignition start, if the coolant temperature is lower than a predetermined temperature value.

In yet another embodiment, the control portion may drive the motorized water pump at a second speed if the cooling fan is operated at a low speed, and if the cooling fan is turned off, the control portion drives the motorized water pump at a first speed that is slower than the second speed.

In another embodiment, the control portion may drive the motorized water pump at a third speed that is faster than the second speed if the cooling fan is driven at a high speed. In a further embodiment, if the vehicle speed exceeds a predetermined value, the control portion increases the driving speed of the motorized water pump according to a factor value of the vehicle speed.

In another embodiment, a motorized water pump control method of a hybrid vehicle may also include suspending operation of a motorized water pump in a condition in which the coolant temperature is less than a predetermined value until a cooling fan is operated, and controlling a driving speed of the motorized water pump according to a load of the cooling fan while the cooling fan is being operated.

In another embodiment, the motorized water pump may be driven at a second speed while the cooling fan is being driven at a low speed.

In yet another embodiment, the motorized water pump may be driven at a first speed that is slower than the second speed while the cooling fan is halted.

In a further embodiment, the motorized water pump may be driven at a third speed that is faster than the second speed if it is determined that the cooling fan is being operated at a high speed, and it is determined that the engine is in a high load condition based on a coolant flux that is determined.

In one embodiment, a factor value according to the vehicle speed may be applied to drive the motorized water pump faster than the third speed if the cooling fan is driven at a high speed, the vehicle speed exceeds a predetermined vehicle speed value, and it is determined that the engine is in a high speed and high load condition.

In another embodiment, the speed of the motorized water pump may be varied according to the vehicle speed in the high speed or high load condition of the engine such that the speed of the motorized water pump is increased or decreased proportionally.

In yet another embodiment, the coolant may be optimally circulated according to driving conditions and a vehicle speed such that the engine is not overheated or overcooled.

In another embodiment, an interior can be heated by a heater in the event that the vehicle enters into an EV mode or an idle engine stop mode.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the subject invention pertains will more readily understand how to make and use the devices and methods of the subject invention, preferred embodiments thereof will be described in detail herein below with reference to the drawings, wherein:

FIG. 1 is a schematic diagram showing a motorized water pump control apparatus of a hybrid vehicle according to one embodiment of an apparatus according to the present invention;

FIG. 2 is a flowchart, corresponding to the schematic diagram in FIG. 1, showing a motorized water pump control procedure of a hybrid vehicle according to an embodiment of a method according to the present invention;

FIG. 3 is a schematic diagram showing a motorized water pump control of a hybrid vehicle according to another embodiment of an apparatus according to the present invention;

FIG. 4 is a flowchart corresponding to the schematic diagram in FIG. 3, showing a motorized water pump control procedure of a hybrid vehicle according to another embodiment of an apparatus of the present invention; and

FIG. 5 is a graph, corresponding to the flowchart of FIG. 4, showing motorized water pump control timing of a hybrid vehicle according to an embodiment of the present invention.

DESCRIPTION OF SYMBOLS

-   -   100: engine     -   110: thermostat     -   120: radiator     -   121: cooling fan     -   130: coolant temperature sensor     -   140: motorized water pump     -   150: control portion

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described for purposes of illustration.

As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention, and the drawings and description are to be regarded as illustrative in nature and not intended to restrict the scope of the invention to the particular examples described herein.

Turning to FIG. 1, a schematic diagram of a motorized water pump control apparatus of a hybrid vehicle according to one embodiment of the present invention is shown. The present invention includes an engine 100, a thermostat 110, a radiator 120, a coolant temperature sensor 130, a motorized water pump 140, and a control portion 150.

In accordance with this exemplary embodiment, the thermostat 110 determines a circulation path of coolant to a bypass line or the radiator 120 according to the coolant temperature exhausted from the engine 100.

The radiator 120 emits heat of the coolant through a contact area of a core thereof to air, and a cooling fan is disposed at one side of the core so as to forcibly blow the air through the core based on the coolant temperature and a driving condition of a vehicle.

The coolant temperature sensor 130 detects the temperature of the coolant flowing into the engine 100 through the radiator 120 or the bypass line, and transmits the detected signal to the control portion 150.

The motorized water pump 140 is disposed between the engine 100 and the thermostat, and is turned on or off. The operating speed is controlled by the control signal which determines whether or not to circulate the coolant.

Typically, the motorized water pump 140 is one of a clutch type or an electric type.

The control portion 150 determines whether the vehicle enters into an EV mode or an idle engine stop mode from an HV mode. If the vehicle enters into the EV mode or the idle engine stop mode in a condition where the coolant temperature has exceeded a predetermined value, the control portion 150 drives the motorized water pump 140 so as to circulate the coolant through the engine 100. In this situation, the motorized water pump 140 drives circulation of the coolant regardless of the operation of the engine 100, so that the engine does not overheat.

In addition, the control portion 150 may drive the motorized water pump 140 to regularly circulate the coolant so that an interior room of the vehicle can be heated based on a heating demand in a case where the vehicle has entered into the EV mode or the idle engine stop mode.

In accordance with an embodiment of the present invention, if the vehicle enters into the idle engine stop mode or the EV mode when the coolant temperature detected by the temperature sensor 130 has exceeded a predetermined value, typically approximately 90° C. to 96° C., the control portion 150 applies a factor value mapped according to the vehicle speed to variably control the motorized water pump 140 and to offer optimized cooling efficiency. If the coolant temperature detected by the temperature sensor 130 is less than the predetermined value, the control portion 150 turns off the motorized water pump 140.

Also, in a further embodiment, if an error is detected from the cooling system, the control portion 150 outputs an alarm signal and simultaneously enters into a limp home mode so as to continuously operate the motorized water pump 150 so that the coolant can circulate in the engine.

Turning to the steps of FIG. 2, the control portion 150 analyzes driving signals detected by sensors step S101, diagnoses the cooling system step S102, and determines whether the diagnosed result is normal or not step S103.

If it is determined that the cooling system is in an abnormal condition step S103, then the control portion 150 outputs an alarm signal in a predetermined method, and enters into the limp home mode so as to continuously operate the motorized water pump 150 so that the coolant is steadily circulated through the engine step S104.

If it is determined that the cooling system is in a normal condition step S103, then the control portion 150 recognizes an on or off condition of a heater switch step S105 to determine whether a heating device is on in step S106.

If it is determined that the heating apparatus is turned on step S106, the motorized water pump 140 is driven, irrespective of the coolant temperature step S107 in order to circulate the coolant such that the interior temperature can be raised step S108.

If the heating apparatus is not turned on step S106, then a driving mode is determined step S109, and it is then determined whether the vehicle enters into the EV mode or the idle engine stop mode from the HV mode step S110.

If it is determined that the hybrid vehicle enters into the EV mode or the idle engine stop mode step S110, then it is determined whether the coolant temperature exceeds a predetermined value (about 90° C. to 96° C.) step S111, step S112.

However, if the coolant temperature is less than the predetermined value step S112, then the motorized water pump 140 is turned off to reduce a load of the engine 100 or a battery, reducing fuel consumption step S113.

If the coolant temperature exceeds a predetermined value in step S112, the motorized water pump 140 is uniformly driven so as to circulate the coolant step S114.

While the motorized water pump 140 is being driven to circulate the coolant, it is determined whether the speed of the vehicle exceeds a predetermined value step S115.

If it is determined that the speed of the vehicle exceeds a predetermined value step S115, then a predetermined factor value according to the speed of the vehicle is applied to the operation speed of the motorized water pump 140 and the operation speed is determined step S116.

After this, the control portion 150 variably controls the motorized water pump 140 at a speed determined by the vehicle speed to circulate the coolant through the engine step S117. In this case, it is desirable that the higher the vehicle speed, the faster the operation speed of the motorized water pump.

Accordingly, the motorized water pump is controlled to be turned on or off according to the coolant temperature in a case that the engine is turned off depending on the mode change of the hybrid vehicle in the present invention so that the engine is stabilized to improve operating efficiency.

Also, if the heating apparatus is turned on regardless of an on or off condition of the engine, the coolant is circulated by the motorized water pump to heat the interior room, thereby improving the reliability of the hybrid vehicle.

FIG. 3 is a schematic diagram showing a motorized water pump control apparatus of a hybrid vehicle according to another exemplary embodiment of the present invention.

This embodiment of the present invention includes an engine 100 as a power source, a thermostat 110, a radiator 120, a motorized water pump 140, and a control portion 150.

Here, the thermostat 110 determines a circulation path of the coolant according to the coolant temperature exhausted from the engine 100 to a bypass line or the radiator 120 so that coolant is circulated through the engine 100.

A coolant temperature sensor 130 detecting the coolant temperature is disposed inside the thermostat, and the coolant temperature detected by the coolant temperature sensor 130 is transmitted to the control portion 150.

The radiator 120 raises the contact area of the coolant to the air through a core thereof in order to emit heat energy of the coolant into the air.

A cooling fan 121 is disposed at one side of the radiator 120 so as to forcibly blow the air through the radiator 120. The cooling fan 121 is operated at a low or high speed by the control portion 150 according to the coolant temperature and the driving condition, based on whether the coolant temperature is higher than a predetermined value.

The motorized water pump 140 is disposed between the engine 100 and the thermostat 110 to be turned on or off depending on the control signal transmitted from the control portion 150, so that the operation speed of the control portion 150 is variably controlled to optimize circulation of the coolant.

Typically, the motorized water pump 140 is one of a clutch type or an electric type.

The control portion 150 is configured to determine a coolant flux according to a load of the cooling fan 121 forcibly blowing the air through the radiator 120. The control portion turns the motorized water pump 140 on or off and variably controls the operation speed of the motorized water pump 140.

In this embodiment, the control portion 150 may determine the outside temperature, engine speed, and coolant temperature detected by the coolant temperature sensor 130 in order to determine driving conditions and the environmental state of the engine 100. If an error is detected from the diagnosed conditions, the engine 100 outputs an alarm signal and simultaneously enters into a limp home mode such that the coolant is continuously circulated by the motorized water pump 140.

The control portion 150 stops operation of the motorized water pump 140 until the cooling fan 121 is operated to cool the radiator 120 in order to shorten a warming up period of the engine and an activation period of an exhaust catalyst in a case that the engine is started in a cold state.

If the cooling fan 121 is operated for the first time after ignition start, the control portion 150 drives the motorized water pump 140 at a second driving speed according to the determined coolant flux. If the cooling fan 121 again stops after the first operation, the motorized water pump 140 is uniformly operated at a first driving speed to circulate the coolant until the cooling fan is operated once more.

In a case that the cooling fan 121 is driven at a high speed, the control portion 150 determines the coolant flux according to the fan speed to drive the motorized water pump 140 in a third driving speed. If the vehicle speed exceeds a predetermined value, the control portion 150 applies a factor value according to the vehicle speed to compensate the driving speed of the motorized water pump 141 so that the coolant flux can be raised.

Turning to FIG. 4, according to another embodiment of the present invention, the control portion 150 detects atmospheric temperature, engine speed, and coolant temperature through the coolant temperature sensor 130 step S101, and determines whether the engine 100 is warmed up or not step S102.

If it is determined that the engine 100 is in a cold state step S102, the control portion 150 stops operation of the motorized water pump 140 so as to warm up the engine step S103. In this case, a water jacket of the engine 100 functions as a thermos to help the engine 100 quickly warm up.

In a condition that the motorized water pump 140 is turned off, the control portion 150 monitors the operating condition of the cooling fan 121 for blowing the air through the radiator 120 step S104, and determines whether the cooling fan is operating step S105.

If the cooling fan 121 sustains its “off” condition step S105, the operation is returned step S103 to repeat the above procedures. If it is determined that the cooling fan 121 is operating at a predetermined low load, the necessary coolant flux is determined by the load of the cooling fan 121 step S106 and the control portion drives the motorized water pump 140 at a second speed to circulate the coolant such that the engine 100 securely sustains its condition in a low load condition of the cooling fan step S107.

Then, it is determined whether the cooling fan 121 stops operating or not step S108.

If it is determined that the cooling fan 121 is operating step S108, the operation is returned to step S107 such that the motorized water pump 140 is driven at a second speed to circulate the coolant. If it is determined that the cooling fan 121 stops operating step S108, the control portion 150 drives the motorized water pump 140 at a first speed that is determined by repeated experiments. In this instance, the first speed is slower than the second speed, such that a coolant flux is lower than when the cooling fan is operated step 109.

In a condition that the motorized water pump 140 is continuously driven at a first speed, it is determined whether the cooling fan 121 is operated at a high speed step S110.

If it is determined that the cooling fan 121 is driven at a high speed step S110, the necessary coolant flux is determined step S111, and the control portion drives the motorized water pump 140 at a third speed to circulate a large amount of coolant so that the temperature of the engine 100 is securely controlled step S112.

While the motorized water pump 140 is driven at the third speed as stated above, it is determined whether the vehicle speed exceeds a predetermined value step S113. In one embodiment, the predetermined vehicle speed value is approximately, 80 Km/h.

If the vehicle speed does not exceed a predetermined value step S113, the operation is returned step S112 to drive the motorized water pump 140 at a third speed. If the vehicle speed exceeds the predetermined value, the control portion applies a factor value according to the high speed of the vehicle step S114, determines a final flux of the coolant, and compensates the driving speed of the motorized water pump 140 so as to circulate the coolant according to a high speed and a high load of the engine step S115.

Operations of this invention including the functions as described above will hereinafter be described in detail with reference to FIG. 5.

Turning to FIG. 5, if the engine 100 is started, the motorized water pump (EWP load) is turned off in order to quickly warm up the engine such that the coolant is not circulated. If the cooling fan is driven at a low speed, the control portion drives the motorized water pump (EWP load) at a second speed P2 to circulate the coolant.

After that, since the coolant temperature is decreased by the operation of the cooling fan, the cooling fan is turned off in order to uniformly sustain the coolant temperature, and the motorized water pump (EWP load) is driven at a first speed P1 to circulate the coolant.

Further, if the cooling fan is operated at a high speed, it is determined that the engine is in a high load condition, and the control portion drives the motorized water pump (EWP load) at a third speed P3 in order to circulate a greater amount of coolant so that the engine temperature is securely controlled.

In one embodiment, in a condition where the motorized water pump (EWP load) is driven at the third speed P3 according to the high load operation of the engine, if it is determined that the vehicle speed exceeds a predetermined vehicle speed value, the control portion applies a vehicle speed factor to determine a final coolant flux, and drives the motorized water pump at a speed that is faster than the third speed such that the engine temperature is securely controlled by a large amount of circulation of the coolant.

In the high speed and high load driving condition, the speed of the motorized water pump is varied according to the vehicle speed such that the coolant circulation amount is proportionally increased or decreased.

In a situation where the engine is started in a cold state, the present invention provides decreased warming time and exhaust catalyst activation time, decreased entry time into the EV mode and the idle engine stop mode, decreased fuel consumption, and overall improvement in the exhaust gas quality.

In addition, because the subject invention provides circulation of the coolant based on the driving conditions, overheating of the engine is provided and driving stability and reliability are improved.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A motorized water pump control apparatus of a hybrid vehicle, comprising: a thermostat determining a circulation path of a coolant; a coolant temperature sensor detecting a coolant temperature; a motorized water pump configured to pump the coolant; and a control portion for controlling the motorized water pump to circulate the coolant, if the vehicle enters into an EV mode or an idle engine stop mode in a condition that the coolant temperature exceeds a predetermined temperature value.
 2. The motorized water pump control apparatus of claim 1, wherein the control portion drives the motorized water pump, if an operation of a heating apparatus is demanded, in the EV mode or the idle engine stop mode.
 3. The motorized water pump control apparatus of claim 1, wherein the control portion varies a driving speed of the motorized water pump according to a vehicle speed, if the vehicle enters into the idle engine stop mode in a condition that the coolant temperature exceeds the predetermined temperature value.
 4. The motorized water pump control apparatus of claim 1, wherein the control portion enters into a limp home mode, outputs an alarm message, and drives the motorized water pump to circulate the coolant if an error is detected.
 5. A motorized water pump control method of a vehicle, comprising: determining whether a vehicle enters into an EV mode or an idle engine stop mode; determining whether a coolant temperature exceeds a predetermined value if the vehicle is in the EV mode or the idle engine stop mode; driving a motorized water pump if the coolant temperature exceeds the predetermined temperature value; turning off the motorized water pump if the coolant temperature is less than the predetermined temperature value; and varying a driving speed of the motorized water pump according to a vehicle speed if the vehicle speed is larger than a predetermined vehicle speed value when the motorized water pump is in operation.
 6. The motorized water pump control method of claim 5, wherein the motorized water pump is driven to circulate the coolant if operation of a heating apparatus is demanded in the EV mode or the idle engine stop mode.
 7. A motorized water pump control apparatus of a hybrid vehicle, comprising: a thermostat determining a circulation path of coolant according to a coolant temperature exhausted from an engine; a radiator emitting heat absorbed in the coolant; a cooling fan disposed at one side of the radiator to blow air; a motorized water pump disposed between the engine and the thermostat to circulate the coolant; and a control portion that varies an on or off mode of the motorized water pump according to an operating load of the cooling fan.
 8. The motorized water pump control apparatus of claim 7, wherein the control portion monitors data relating to environmental and driving conditions of the engine and enters into a limp home mode so as to operate the motorized water pump if an error is detected from the monitored data.
 9. The motorized water pump control apparatus of claim 7, wherein the control portion stops operation of the motorized water pump until the cooling fan is operated a first time after ignition, if the coolant temperature is lower than a predetermined temperature value.
 10. The motorized water pump control apparatus of claim 7, wherein the control portion drives the motorized water pump at a second speed if the cooling fan is operated at a low speed.
 11. The motorized water pump control apparatus of claim 10, wherein the control portion drives the motorized water pump at a first speed that is slower than the second speed if the cooling fan is turned off.
 12. The motorized water pump control apparatus of claim 7, wherein the control portion drives the motorized water pump at a third speed that is faster than the second speed if the cooling fan is driven at a high speed.
 13. The motorized water pump control apparatus of claim 12, wherein the control portion increases the driving speed of the motorized water pump according to a factor value of a vehicle speed if the vehicle speed exceeds a predetermined vehicle speed value.
 14. A motorized water pump control method of a hybrid vehicle, comprising: suspending operation of a motorized water pump in a condition in which a coolant temperature is less than a predetermined temperature value until a cooling fan is operated; and controlling a driving speed of the motorized water pump according to a load of a cooling fan while the cooling fan is being operated.
 15. The motorized water pump control method of claim 14, wherein the motorized water pump is driven at a second speed while the cooling fan is being driven at a low speed.
 16. The motorized water pump control method of claim 15, wherein the motorized water pump is driven at a first speed that is slower than the second speed while the cooling fan is halted.
 17. The motorized water pump control method of claim 15, wherein the motorized water pump is driven at a third speed that is faster than the second speed if it is determined that the cooling fan is being operated at a high speed, and it is determined that the engine is in a high load condition based on a determined value of a coolant flux.
 18. The motorized water pump control method of claim 17, wherein a factor value according to the vehicle speed is applied to drive the motorized water pump faster than the third speed if the cooling fan is driven at a high speed, the vehicle speed exceeds a predetermined value, and it is determined that the engine is in a high speed and high load condition.
 19. The motorized water pump control method of claim 14, wherein the driving speed of the motorized water pump is varied proportionally according to the vehicle speed in the high speed or high load condition of the engine. 